A door may comprise a single heavy slab or a plurality of connected door segments, the sum of which are very heavy. Various means exist to aid in lifting the door, such as counterweights, torsion springs, and lifting cables. These aids effectively counteract the weight of the door which allows it to be easily lifted by manual or mechanical means. In the event any element of the aforementioned means breaks, the door can fall rapidly, causing possible property damage, injury, or even death.
Numerous methods have been employed to stop a door after such a failure, but they are either expensive, complicated, and/or difficult to install without extensive modifications.
U.S. Pat. No. 2,185,828 discloses a safety catch for vertically sliding doors. While this invention purports to be installable on existing door systems, the installation requires removing parts from the existing door and either moving them or substituting other parts. It is also relatively complicated, comprising numerous moving parts which must interact in order to achieve its purpose.
U.S. Pat. No. 5,494,093 discloses a rolling door stop apparatus. This invention is intended primarily to arrest the uncontrolled fall of a rolling door, which, as opposed to an overhead door, is rolled up and down much like a window shade. While this invention could be utilized on an overhead type door, its installation would be difficult and time-consuming if performed on an existing door.
U.S. Pat. No. 6,024,155 discloses a truck doorstop. This invention is intended to prevent a truck-mounted overhead door from falling closed due to sudden motion of the truck. This invention actually redirects the bottom door segment after the door is fully open, forcing the door to move laterally in the event the truck is moved. There is no provision to prevent the door from free-falling during opening or closing, if the counterbalance system fails.